Process for the production of petroleum tar pitch for use as a binder in the production of electrodes

ABSTRACT

A process for the production of petroleum tar pitch with the using a fresh hydrocarbon feedstock, preheating it, treating the heated feedstock and passing fractionating the treated feedstock into gases, light distillates and a bottom fractionation stream, then dividing the bottom fraction stream into a recycle stream and a cracked fraction stream and using the cracked fraction stream in a reduced pressure distillation tower so that the light cracked fraction is fractionated light vacuum gas oil, heavy vacuum gas oil and a high quality petroleum tar pitch.

BACKGROUND OF THE INVENTION

High quality petroleum tar pitch can be used in a variety ofapplications. One of the most important uses for high quality petroleumtar pitch is in the manufacture of anodes made from calcined petroleumcoke and a binder pitch. The anodes are used in the production ofprimary aluminum. Presently anodes for use by the aluminum and steelindustries are manufactured employing almost exclusively coal tar pitchas the binder. There have been many attempts in the past to producepetroleum tar pitch suitable for use as a binder in the manufacture ofelectrodes.

In the metallurgical industry, the electrodes are made from petroleumcoke and pitch binder. Pitch typically requires the presence ofquinoline, and a high residual carbon content. The addition of carbonblack into pitch tar is typically done to increase residual carbon andQuinoline insoluble content.

None of the foregoing processes have been able to produce commercialpetroleum tar pitch suitable for use as a binder in the manufacture ofelectrodes for the aluminum and steel industries. It is highly desirableto provide a process for the production of high quality petroleum tarpitch which would allow for the economic production of pitch suitablefor the manufacture of electrodes.

Further objects and advantages of the present invention will appearhereinbelow.

SUMMARY OF THE INVENTION

The invention is drawn to a process for the production of petroleum tarpitch by first obtaining a fresh hydrocarbon feedstock and then feedingthat feedstock to a pre-heater and thereafter feeding a soaker reactorfor treatment under controlled conditions so as to promote condensationand polymerization reactions. The treated feedstock is thereafter passedto a fractionating tower wherein the feedstock is fractionated intogases, light distillates and bottom fraction, then dividing the bottomfraction stream into a recycle stream and a cracked fraction stream,then feeding the cracked fraction stream to a reduced pressuredistillation tower wherein the cracked fraction stream is furtherfractionated into (1) light vacuum gas oil, (2) heavy vacuum gas oil and(3) a high quality petroleum tar pitch, of a quality suitable for use asa binder in the manufacture of electrodes, the petroleum tar pitch isthen mixed with a refining element such as anode grade coke to improvethe desired petroleum tar pitch product and finally recycling therecycle stream and admixing the recycle stream with the fresh feedstock

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic flow diagram illustrating the process of thepresent invention.

DETAILED DESCRIPTION

The present invention is drawn to a process for the production of highquality petroleum tar pitch for use as a binder in the manufacture ofelectrodes for the aluminum and steel industries. The characteristics ofa high quality petroleum tar pitch are the following:

-   [Conradson Carbon, (wt. %) 40-60-   Density@15° C., (gr/cc) 1.20-1.25-   Mettler Softening Point, (° C.) 100-125-   Quinoline Insoluble, (wt. %) 0-10]

With reference to the FIGURE, as shown a fresh feedstock is deliveredvia line 20 for treatment in the process of the present invention. Thefresh feedstock is preferably a highly aromatic hydrocarbon stream.Feedstocks suitable and preferred for the process of the presentinvention are characterized by the following composition and properties:

-   [Density@15° C., (gr/cc) 0.8-1.15-   Solids Content, (wt. %) 0-0.1-   Aromatics, (wt. %) 54-85].

Suitable hydrocarbon feeds include highly aromatic hydrocarbon selectedfrom the group consisting of catalytic cracking decanted oil, lubricantextract, Heavy Coker Gasoil (HCGO), Heavy Vacuum Gasoil (HVGO) andmixtures thereof.

The fresh feedstock as defined above can, if desired, be delivered to afiltering station 1 wherein the hydrocarbon stream is filtered so as toremove excess undesirable solids so as to produce a filtered cleanstream. In accordance with the present invention it is desired that theproduct treated in the process of the present invention have a solidscontent of between 0 to 0.01 wt. %. By filtering the fresh feed, thedesired solid content can be obtained. Typical filtration techniquessuch as centrifugal, electrostatic or mechanical techniques can be usedin the filtering station 1. These techniques are sufficient to remove atleast 99% of the undesirable solids in the fresh feed stream. Thefiltered stream preferably has the following properties:

-   [Conradson Carbon, (wt. %) 0-7-   Density@15° C., (gr/cc) 0.8-1.1-   Solids Content (wt %) 0-0.01-   Aromatics, (wt. %) 54-85]

The clean filtered stream is thereafter fed via line 21 to a heater 2wherein the stream is pre-heated. It is desirable in the process of thepresent invention to mix the filtered stream with a recycle stream in amanner to be described hereinbelow.

The stream fed to the heater or furnace 2 is pre-heated to a temperatureof between 380° and 480° C. and thereafter is delivered via line 23 to asoaker type reactor 3. The heated feedstock is treated in the soakerreactor 3 at a temperature of from about 360° to 460° C., a pressure offrom about 1480 to 1825 kpa and a residence time of from about 0.25 to 5hours. This treatment allows condensation and polymerization reactionsto take place in the soaker reactor. It is preferred that the treatmentin both the heater furnace and soaker reactor take place in anoxygen-free environment and, preferably an inert environment.

The treated stream from the soaker 3 is delivered via line 24 to afractionating tower 4 where the feedstock is fractionated into gases,which are taken off via line 25, light distillates which are taken offvia line 26 and a bottom fraction stream which is taken off via line 27.The fractionator is operated under the following operating conditions: abottom fractionator temperature of from about 330° to 430° C. and apressure of from about 101 to 850 kPa.

The yields from the fractionating tower 4 comprises 2 to 8 wt. % C4-gases and 3 to 8 wt. % light distillates having an ASTM D-86 cut pointof between 92° C. and 220° C. based on fresh feed. It is preferred thatthe treatment in the fractionating tower 4 take place in an oxygen freeenvironment and, preferably, an inert environment.

The bottom fraction drawn off through line 27 is a cracked fractionbottom stream having the following composition and properties:

-   [Conradson Carbon, (wt. %) 10-18-   Density@15° C., (gr/cc) 1.1-1.15-   Solids Content, (wt. %) 0-0.01-   Aromatics, (wt. %) 70-95-   Softening Point, (° C.) <25]

In the preferred embodiment of the present invention, a portion of thecracked fraction bottom stream is recycled back to heater 2 or soakerreactor 3 and the remainder is further fractionated in the mannerdiscussed hereinafter.

The portion of cracked fraction forming the recycle stream is preferablyrecycled via line 28 where it is admixed with the fresh feed prior todelivery of the feed to the furnace 2. In accordance with the presentinvention, the recycle delivered via line 28 is mixed with the freshfeed in a ratio of up to 3:1 by volume of recycle to fresh feed andpreferably in a ratio of about between 2:1 to 3:1. Recycling of theheavy cracked fraction via line 28 is highly desirable in order tooptimize the resulting pitch properties obtained in the process of thepresent invention upon further fractionation.

The remainder of the cracked fraction is delivered via line 29 to afurther fractionating unit 5 such as a reduced pressure distillationtower wherein the cracked fraction is further fractionated into lightvacuum gas oil taken off via line 30, heavy vacuum gas oil taken off vialine 31 and petroleum tar pitch taken off line 33. The cracked fractionis fractionated in distillation unit 5 at a bottom fractionatortemperature of between 300° to 380° C. and a pressure of between 0.3 to15 kPa and preferably in an oxygen-free environment. The petroleum tarpitch resulting from the process of the present invention and drawn offvia line 33 is a high quality petroleum pitch having the followingproperties:

-   [Conradson Carbon, (wt. %) 40-60-   Density@15° C., (gr/cc) 1.20-1.25-   Mettler Softening Point, (° C.) 100-125-   Quinoline Insoluble, (wt. %) 0-10]

This petroleum tar pitch is of high quality and suitable for use as abinder in the manufacture of electrodes.

The yield of light vacuum gas oil taken off line 30 is between 15 to 25wt. %, the yield of heavy vacuum gas oil taken off line 31 is from 30 to50 wt. % and the yield of petroleum tar pitch taken off line 33 isbetween 10 to 50 wt. % with all yields being based on fresh feed. Thelight vacuum gas oil has an ASTM D-86 end boiling point of between 300°to 360° C. and the heavy vacuum gas oil has an ASTM D-1160 end boilingpoint of between 450° to 570° C.

The petroleum tar pitch taken off via line 33 can, if desired, bedelivered to a mixer 6 where it is mixed with an additive selected fromthe group consisting of fine divided anode grade coke, carbon black, ormixtures thereof via line 36. In accordance with the present inventionit is desirable to use the light vacuum gas oil taken off line 30 andheavy vacuum gas oil taken off line 31 as the additive to the mixture 6.It is preferred that the light vacuum gas oil or the heavy vacuum gasoil be mixed with the pitch in an amount of between 3 to 15 volumepercent. The preferred light vacuum gas oil has the followingcomposition and properties:

-   [ASTM D-86 Initial Boiling Point, ° C. 170-220-   ASTM D-86 Final Boiling Point, ° C. 300-360-   API Gravity 18-28-   Aromatics, wt. % 45-80]    The preferred heavy vacuum gas oil has the following composition and    properties:-   [ASTM D-1160 Initial Boiling Point, ° C. 240-390-   ASTM D-1160 Final Boiling Point, ° C. 450-580-   API Gravity 1-4-   Aromatics, wt. % 45-80]

The heavy vacuum gas oil can also be recycled into the filteredfeedstock in a ratio of at least about 0.25:1 by volume recycle streamto fresh feedstock, but preferably a ratio of about between 0.5:1 to0.8:1 by volume recycle stream to fresh feedstock.

A finely divided anode grade coke, carbon black, or mixtures thereof isadmixed with the petroleum pitch in mixer 6. The proportion of the anodegrade coke, carbon black, or mixtures thereof mixed with the petroleumpitch should be between 5 to 20 wt. %. Suitable anode grade coke, carbonblack, or mixtures thereof for use in the process of the presentinvention has the following properties:

-   [Average Particle Size, microns 12-110-   Apparent Bulk Density, gr/cc 0.46-0.65-   Water Content, wt. % 0-0.2-   Oil Absorption, cc/100 gr 60-75]

The refining additives delivered via line 36 to mixer 6 have the effectto increase Quinoline insoluble content, conradson carbon and softeningpoint. An additive of light vacuum gas oil or heavy vacuum gas oilimproves the wettability of the pitch which would reduce the temperatureand mixing time necessary when mixed with calcining petroleum cokeduring the manufacture of electrodes. The modified petroleum pitchproduct can be delivered via line 34 to a finishing station 7 where itis shaped as pencils or flakes prior to being sent to storage via line35.

The use of anode grade coke as additive refined with the heavy vacuumgasoil showed improvements in the anodes properties. The use of anodegrade coke of the present invention is preferred for multiple reasons.The availability of the product, the low nickel and vanadium content,and the fact that it does not add other foreign agents to the anode. Theproduct performed well during mixing and therefore resulted in excellentquality aluminum. It is for these reasons that anode grade coke waschosen as the preferred refining element

Further, in order to decrease the deposition of solids, a reduction ofresidence time was implemented and an additional recycling of a cleanerstream with less contaminant content was introduced through line 32.

The process of production of tar pitch is a moderate thermal crackingprocess, which uses polymerization reactions, cracking and condensationto transform the load in a binder. The recycling step is importantbecause it increases the conversion rate and the production of binderpitch.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications, which are within its spirit and scope as defined bythe claims.

What is claimed is:
 1. A process for the production of petroleum tarpitch comprising: a. providing a fresh hydrocarbon feedstock; b.pre-heating at least a portion of the feedstock in a furnace to atemperature of about 380° to 480° C.; c. feeding at least a portion ofthe heated feedstock to a reactor and treating at least a portion of theheated feedstock in the reactor under controlled conditions so as topromote condensation and polymerization reactions; d. passing at least aportion of the treated feedstock to a fractionating tower wherein atleast a portion of the treated feedstock is fractionated into (1) gases,(2) light distillates and (3) a bottom fractionation stream; e. dividingthe bottom fraction stream into a recycle stream and a cracked fractionstream; f. feeding the cracked fraction stream to a reduced pressuredistillation tower wherein the light cracked fraction is furtherfractionated into (1) light vacuum gas oil, (2) heavy vacuum gas oil and(3) a high quality petroleum tar pitch; g. recycling the recycled streamand admixing the recycle stream with the fresh feedstock; and h. mixingthe petroleum tar pitch with a refining element in the form of anodegrade coke, to create a petroleum tar pitch product.
 2. A processaccording to claim 1 wherein the feedstock is a highly aromatichydrocarbon selected from the group consisting of catalytic crackingdecanted oil, lubricant extract, Heavy Coker Gasoil (HCGO), Heavy VacuumGasoil (HVGO) and mixtures thereof and has the following composition andproperties: [Density@15° C., (gr/cc) 0.8-1.15 Solids Content, (wt. %)0-0.1 Aromatics, (wt. %) 54-85].
 3. A process according to claim 1wherein the light vacuum gas oil has the following properties: [ASTMD-86 Initial Boiling Point, ° C. 170-220 ASTM D-86 Final Boiling Point,° C. 300-360 API Gravity 18-28 Aromatics, wt. % 45-80].
 4. A processaccording to claim 1 wherein the heavy vacuum gas oil has the followingproperties: [ASTM D-1160 Initial Boiling Point, ° C. 250-320 ASTM D-1160Final Boiling Point, ° C. 450-520 API Gravity 0-9 Aromatics, wt. %45-95].
 5. A process according to claim 1 wherein the petroleum tarpitch has the following properties: [Conradson Carbon, (wt. %) 40-60Density@15° C., (gr/cc) 1.20-1.25 Mettler Softening Point, (° C.)100-125 Quinoline Insoluble, (wt. %) 0-10].
 6. A process according toclaim 1 wherein the refining element added is anode grade coke and it isadded in an amount of between 5 to 20 wt. % of the petroleum pitch.
 7. Aprocess according to claim 1 wherein the finely divided anode grade cokehas the following properties: [Average Particle Size, microns 12-110Apparent Bulk Density, gr/cc 0.46-0.65 Water Content, wt. % 0-0.2 OilAbsorption, cc/100 gr 60-75].
 8. A process according to claim 1 whereinthe petroleum tar pitch product is delivered to a finishing station tobe shaped.
 9. A process according to claim 1 wherein at least a portionof the feedstock is filtered to produce a feedstock having a solidcontent of 100 ppmw.
 10. A process according to claim 9 wherein thefiltering is done by centrifugal, electrostatic or mechanicaltechniques.
 11. A process according to claim 9 wherein the filteringremoves at least 99% of solids.
 12. A process according to claim 9wherein the filtered feedstock has the following composition andproperties: [Conradson Carbon, (wt. %) 0-7 Density@15° C., (gr/cc)0.8-1.1 Solids Content (wt %) 0-0.01 Aromatics, (wt. %) 54-85].
 13. Aprocess according to claim 9 wherein the filtered feedstock is heated toa temperature of between 380 and 480° C. to provide a heated feedstock.14. A process according to claim 13 wherein the heated feedstock ispassed to a soaker reactor, plug flow reactor or batch reactor, andwherein the feedstock is treated in the reactor at condensation andpolymerization conditions to provide a treated feedstock.
 15. A processaccording to claim 14 wherein the conditions include a temperaturebetween 360 and 460° C., a pressure between 1480 and 1825 kpA, theconditions are oxygen free and inert and are held between 0.25 and 5hours.
 16. A process according to claim 14 wherein the treated feedstockis passed to a fractionating tower wherein the treated feedstock isfractionated into (1) gases, (2) light distillates and (3) a bottomstream.
 17. A process according to claim 1 wherein step (d) takes placeunder the following conditions: [Temperature, ° C. 330-430 Pressure, kPa101-850 in an inert environment and substantially oxygen free].
 18. Aprocess according to claim 16 wherein the treated feedstock isfractionated to yield: 2 to 8 wt. % C₄-gases 3 to 8 wt. % lightdistillates having an ASTM D-86 cut point of between 92° C. and 220° C.based on fresh feed and a bottom stream.
 19. A process according toclaim 16 wherein the bottom stream is divided into a recycle stream anda cracked fraction bottom stream.
 20. A process according to claim 19wherein the cracked fraction bottom stream has the following compositionand properties: [Conradson Carbon, (wt. %) 10-18 Density@15° C., (gr/cc)1.1-1.15 Solids Content, (wt. %) 0-0.01 Aromatics, (wt. %) 70-95Softening Point, (° C.) <25].
 21. A process according to claim 19wherein the recycle stream is admixed with the filtered feedstock in apreferred ratio of between 2:1 and 3:1 by volume of recycle stream tofresh feedstock.
 22. A process according to claim 19 wherein the recyclestream is mixed with the filtered feedstock.
 23. A process according toclaim 19 wherein the recycle stream is mixed with the filtered feedstockin a ratio of up to 3:1 by volume recycle stream to fresh feedstock. 24.A process according to claim 19 wherein the cracked bottom stream isfurther fractionated to yield Light Vacuum Gas Oil, Heavy Vacuum Gas Oiland a high quality petroleum tar pitch.
 25. A process according to claim24 wherein the cracked bottom stream is further fractionated under thefollowing conditions: bottom fractionator temperature 300-380° C.,0.3-15 kPa pressure, in an inert and a substantially oxygen freeenvironment.
 26. A process according to claim 24 wherein the crackedbottom stream is further fractionated to yield the following products:[ASTM D-1160 End Point Wt. % Light Vacuum Gas Oil 300-360° C. 15-25Heavy Vacuum Gas Oil 450-570° C. 30-50 Petroleum Tar Pitch 15-50].
 27. Aprocess according to claim 24 wherein the Heavy Vacuum Gas Oil isrecycled into the filtered feedstock in a ratio from about 0.25:1 byvolume recycle stream to fresh feedstock.
 28. A process according toclaim 24 wherein the heavy vacuum gas oil is recycled into the filteredfeedstock in a ratio of about between 0.5:1 to 0.8:1 by volume recyclestream to fresh feedstock.
 29. A process according to claim 1 whereinthe refining element further comprises fine divided carbon black.
 30. Aprocess according to claim 1 wherein the refining element furthercomprises anode grade coke and low metals and sulfur content coke.